The reproductive organs of both male and female European lobsters (Homarus gammarus) are H-shaped gonads that lie dorsal to the gut on the large hepatopancreas. The ovary consists of a pair of tubular, parallel lobules with a connecting bridge. The germarium of the ovary containing oogonia is concentrated in the center of the ovarian lobe. As oogonesis proceeds, the oocytes move to the peripheral regions of the ovary. The follicle cells begin to surround the oocytes in the previtellogenic stage, and the mature oocytes are completely surrounded by the follicle cells. Carbohydrates exist in both early and late vitellogenic oocytes that give PAS positive reaction. However, their rising protein content in late vitellogenic oocytes makes them stain with Bromophenol blue. Testes show convoluted lobules with a germinal epithelium and a central collecting duct, and the paired vasa deferentia have three distinct parts. Spermatophores are nonpedunculate and tubular, which extrude as a continuous column and consist of a sperm mass covered with primary and secondary layers. The primary layer stains with Bromophenol Blue and gives a PAS positive reaction. But the secondary layer only weakly stains with Bromophenol Blue. The histochemical results may indicate that the function of the two layers is different.